The invention relates to CVT pulleys, and more particularly to continuously variable diameter pulleys where the effective diameter of the pulley is continuously and infinitely adjustable between a maximum and minimum position.
A primary means of connecting a power source, such as an engine, to a driven load is with a gear type transmission. Such transmissions generally comprise a series of gears, each having a different gear ratio. For example, transmissions may have a single gear or may comprise several gears. Each gear is selected by a user by first engaging a clutch. The clutch mechanism temporarily disengages the gear train so a user can select a gear. The clutch is then released, the gears are engaged and the power is transmitted to the driven load.
A limitation of this type of system is that only a certain set of gear ratios is available to a user. The gear ratio range is usually predetermined based upon the anticipated use of the equipment. It is not easily or inexpensively changed by a user. Further, most engines have a particular operating range where efficiency is maximized. Generally, only a single gear will fall near or on the most efficient operating point. The other gears usually result in relatively inefficient operation of the engine.
In order to increase the available range of gear ratios, the continuously variable transmission addresses the need for more gears. The continuously variable transmission, or CVT, generally comprises a driver pulley connected to a power source and a driven pulley connected to a load. A flexible element such as a belt or chain connects the pulleys and transmits the power from the driver to the driven. The position of the surface on which the belt runs in the pulley is referred to as the effective diameter, xcfx86. The speed of the driven pulley may be changed by varying the effective diameter of the driver pulley and the driven pulley. Changing the effective diameter of the pulleys will result in a corresponding change in the speed of the driven pulley. This is based upon a linear relationship between the pulleys and the ratio of the effective diameters of each. It is the ratio of the effective diameters of each pulley that determines the power transmission characteristics of the CVT. Therefore, a key element of the CVT is the variable pulley mechanism.
Various forms of continuously variable pulleys are known in the art. FIG. 2 represents a prior art flat belt CVT pulley, U.S. Pat. No. 4,024,772 to Kumm. Driver sheaves 6 transmit power to blocks 9 through a number of axially spaced sets of oppositely inclined radial grooves 11 and then to belt 7. Belt 7 is trained about blocks 10 on driven sheaves 8 through a number of axially spaced sets of oppositely inclined radial grooves 12. FIG. 2 is depicted in an under-drive condition where the effective diameter of the driver pulley is less than the effective diameter of the driven pulley.
FIG. 3 depicts a prior art CVT with conical driver sheave 13 and driven sheave 15 connected by v-belt 14. The sheave sections are connected to a coaxial shaft. At least one of the sheave sections moves axially on the shaft. Movement of the sheave section causes the effective diameter of the pulley to change, which causes the radius at which the belt runs on the pulley to change. The radius of operation for the driver pulley and the driven pulley establishes the gear ratio of the transmission.
In FIG. 4, prior art v-belt 14 has a load bearing tensile member 16. The v-belt 14 has a series of transverse blocks 17 connected along its body. Blocks 17 have inclined surfaces 19 which contact the inner surfaces of the sheave sections. Retaining rods 18 attach the blocks to the v-belt body.
Another form of continuously variable pulley is disclosed in U.S. Pat. No. 5,492,506 to Lorance. A plurality of vanes having an outer circumferential drive surface are moveable radially outward. A cone which is moveable axially cooperates with beveled ends of the vanes. Axial movement of the cone presses against the beveled ends which forces the vanes outward. The drive surface comprises parallel teeth which cooperate with a toothed belt.
The disadvantages of the prior art designs include reduced ability to transmit high torque resulting in low load capacity; relatively complicated sheave design or belt design; excess heat being generated in the belt during operation caused by friction between the belt sides and the sheaves; high cost because of parts and assembly time of the pulleys; excessive noise caused by large pitch and corresponding low number of belt blocks; high belt wear giving low durability for both designs. FIG. 3 has a limited overall ratio due to heat build-up. The prior art designs generally have a large transmission mass and size.
What is needed is a CVT pulley that uses a readily available belt configuration. What is needed is a CVT pulley having reduced contact pressure on the belt blocks resulting in low heat generation. What is needed is a CVT pulley with increased load carrying capacity. What is needed is a CVT pulley that generates less noise. What is needed is a CVT pulley with reduced size. What is needed is a CVT pulley with reduced cost. What is needed is a CVT pulley with an increased overall ratio. What is needed is a CVT pulley with reduced requirements for material strength in the design. What is needed is a CVT pulley with reduced axial force to simplify the control mechanism. What is needed is a CVT pulley with increased life by reduction of wear of frictional components. The present invention meets these needs.
The primary aspect of the present invention is to provide an improved CVT pulley.
Another aspect of the invention is to provide a CVT pulley that uses a multi-ribbed v-belt.
Another aspect of the present invention is to provide a CVT pulley having reduced contact pressure on the belt blocks resulting in low heat generation.
Another aspect of the present invention is to provide a CVT pulley having increased load carrying capacity.
Another aspect of the present invention is to provide a CVT pulley having less noise.
Another aspect of the present invention is to provide a CVT pulley having reduced size.
Another aspect of the present invention is to provide a CVT pulley having reduced cost.
Another aspect of the present invention is to provide a CVT pulley having an increased overall ratio.
Another aspect of the present invention is to provide a CVT pulley having reduced requirements for material strength in the design.
Another aspect of the present invention is to provide a CVT pulley having reduced axial force to simplify CVT control mechanism.
Another aspect of the present invention is to provide a CVT pulley having increased life by reduction of wear of frictional components.
A further aspect of the invention is variable contact between the belt and belt blocks or elements. Contact areas will be different each time the belt engages the belt blocks.
The cost of the transmission is significantly lower (for example, 119 belt blocks of 4 mm width in the present invention, vs. 148 elements of 5 mm width for the Kumm device).
Other aspects of the invention will be pointed out or made apparent by the following description of the invention and the accompanying drawings.
The invention comprises a continuously variable transmission pulley. The pulley comprises at least one axially moveable sheave section which is coaxial with a second sheave section. Each sheave section has a series of radial grooves which are axially and radially aligned. The radial grooves are arranged in pairs between each sheave section. The belt blocks span between the sheave sections, each having opposing arcuate ends that slidingly engage a pair of grooves. The belt blocks are arranged circumferentially about an axial sheave centerline. Each belt block also has a surface for receiving a multi-ribbed v-belt. At least one elastic member encircles the belt blocks so as to control their relative positions, keeping them in contact with the sheave grooves as the pulley rotates. As the movable sheave is moved axially, each belt block moves radially within its respective grooves so as to increase or decrease the effective diameter of the pulley.